1. Field of the Invention
The present invention relates to a device for detecting a collision of a vehicle when the vehicle is brought into collision, in a short period of time with high reliability and a device for initiating the passenger protecting device.
2. Discussion of the Background
Conventionally, a passenger protecting device such as an air bag etc. is operated by using a collision detecting device for detecting collision of a vehicle from the magnitude of acceleration of the vehicle. A collision detecting device for detecting collision of a vehicle more swiftly and firmly is disclosed in Japanese Unexamined Patent Publication JP-A-4-135947.
FIG. 25 is a block diagram showing a driving circuit of a conventional passenger protecting device for a vehicle, FIG. 26(A) is a diagram showing a change over time in an output of an acceleration sensor in collision and FIG. 26(B) is a diagram showing a displacement of a head portion of a passenger.
In FIG. 25 numeral 69 designates an acceleration sensor for detecting a change in an acceleration caused by collision or the like of a vehicle and outputting the detection result as an analog signal a(t). Numeral 70 designates a first incomplete integrating circuit having a time constant T.sub.1 for integrating the analog signal a(t) outputted from the acceleration sensor 69, and numeral 71 designates a second incomplete integrating circuit having a function the same as that of the first incomplete integrating circuit 70 for processing an incomplete integration output v(t) from the first incomplete integrating circuit again to incomplete integration. The time constant T.sub.2 of the second incomplete integrating circuit 71 is the same as the time constant T.sub.1 of the first incomplete integrating circuit 70.
Numeral 72 designates a first coefficient circuit comprising a first damper for adding a first coefficient to the detected output from the acceleration sensor 69, numeral 73 designates a second coefficient circuit comprising a second damper having a damping rate of K and the second coefficient circuit 73 adds a second coefficient to the incomplete integration output v(t) from the first incomplete integrating circuit 70. Further, the damping rate of the first coefficient circuit 72 is a half of a square of the damping rate K of the second coefficient circuit 73. Incidentally, the above-described damping rate K is equal to a time period td, required from supplying an ignition current to an ignition device of an air bag, mentioned later, to the completion of expansion of the air bag.
Numeral 74 designates an adding circuit and the adding circuit 74 adds an output x(t) from the second incomplete integrating circuit 71, an output from the first coefficient circuit 72 and an output from the second coefficient circuit 73. Numeral 75 designates a comparing circuit switching the output level to, for example, high level when the added output from the adding circuit 74 exceeds a predetermined threshold value, numeral 76 designates a driving circuit, numeral 77 designates an ignition device that is a main body of a passenger protecting device and the ignition device 76 operates, for example, an air bag based on an output from the driving circuit 76.
Next, an explanation will be given of the operation of the conventional device.
First, when a vehicle is running at a constant velocity V0, if the acceleration a(t) operating in the forward and rearward direction of the vehicle as illustrated by FIG. 26(A) is detected by the acceleration sensor 69, the head of the passenger is thrown at the constant speed v0, while the acceleration a(t) at that time is operating also on the passenger, whereby the head starts to move at a relative velocity in respect of the vehicle, that is, v(t) (integral over time of a(t)).
Meanwhile, the output a(t) of the acceleration sensor 69 at that time is integrated by the first incomplete integrating circuit 70. Also, when the position of the head immediately before collision is set to an initial position, the head is displaced by x(t) (integral over time of v(t)) from the initial position following a time-sequential procedure in accordance with the starting of the movement. The displacement x(t) is calculated by integrating the output of the first incomplete integrating circuit 70 by the second incomplete integrating circuit 71 whereby an estimated amount of displacement of the head of the passenger in the actual time is calculated.
Next, the output v(t) from the first incomplete integrating circuit 70 is weighted by td by the second coefficient circuit 73 whereby v(t).times.td, that is, an amount of displacement in a time period of td is calculated. Further, the output a(t) from the acceleration sensor 69 is weighted by 1/2(td.times.td) by the first coefficient circuit 72 whereby 1/2(td.times.td), that is, an amount of displacement in a time period of td is calculated. The outputs are added by the adding circuit 74 whereby x(t)+v(t)td+1/2a(t).times.(td.times.td) is calculated. That is, by this operation a predicted value of x(t+td) for the position of the head of the passenger after the time period of td from the current time point is calculated.
The predicted position is supplied to the comparing circuit 75 and when the position of operating an air bag etc. is set to a position which is dislocated from the initial position by x in FIG. 26(B), the air bag is operated at a time point t1 that is earlier than a time point t2 where the position of the head actually reaches x by the time period of td as illustrated by a curve x(t).
As described above, according to the conventional example the displacement of the head of the passenger is calculated from the acceleration signal in accordance with the above-mentioned equation and when the calculated displacement of the head of the passenger is determined to be equal to or larger than a predetermined amount, the passenger protecting device is operated.
The following problems occur with the conventional passenger protecting device for a vehicle as described above.
(1) In order to shorten the determining time the predicted displacement signal x(t+td)=x(t)+v(t)td+1/2a(t).times.(td.times.td) provided by adding the acceleration and the velocity respectively multiplied by the coefficients to the displacement signal x(t), is calculated. However, the predicted displacement signal x(t+td) is only a value for determining the collision earlier than the normal determination by the displacement of the passenger. Further, the predicted displacement signal x(t+td) is not the value accurately showing the displacement of the passenger and therefore, even in the case where the operation of the passenger protecting device is not necessary, the passenger protecting device may prematuredly be operated whereby the reliability of the collision determination is deteriorated.
(2) The conventional passenger protecting device does not correspond to various collision modes such as front collision, oblique collision, collision to a pillar or the like, running on a road shoulder, running under a large-sized vehicle etc. and the passenger protecting device may be unnecessarily operated or the determination of collision may be retarded depending on the collision mode.
(3) The threshold value at the comparator used in the determination of collision stays constant irrespective of a change over time and cannot sufficiently correspond to various collision modes and the passenger protecting device may unnecessarily be operated or the determination of collision may be retarded depending on the collision mode.
(4) The determination of collision may be retarded in expanding a side air bag corresponding to a collision from a side direction which requires a collision determining time further shorter than that in the front collision in the forward and rearward direction.